Semiconductor device, LED head and method of manufacturing the same

ABSTRACT

A semiconductor device includes a substrate, and a semiconductor thin film bonded to the substrate, wherein the semiconductor thin film includes a plurality of discrete operating regions and an element isolating region which isolates the plurality of discrete operating regions, and the element isolating region is etched to a shallower depth than a thickness of the semiconductor thin film, and is a thinner region than the plurality of discrete operating regions.

This is a Divisional of U.S. application Ser. No. 11/445,241, filed Jun.2, 2006, U.S. Pat. No. 7,625,809 and allowed on Jul. 24, 2009, which wasa Divisional of U.S. application Ser. No. 10/936,701, filed Sep. 9,2004, and issued as a U.S. Pat. No. 7,078,729 on Jul. 18, 2006, thesubject matters of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device formed bybonding a semiconductor thin film such as an LED epitaxial film to asubstrate, to an LED print head using this semiconductor device, to animage-forming apparatus using this LED print head, and to a method ofmanufacturing the semiconductor device.

2. Description of the Related Art

In the conventional art, the electrical connection between an LED chipand a driver IC chip for driving and controlling the LED chip, was madeby a bonding wire (e.g., Japanese Patent Laid-Open Publication No.2001-244543). FIG. 13 is a perspective view schematically showing aconventional semiconductor device wherein an LED chip and a driver ICchip are connected by bonding wires, and FIG. 14 is a perspective viewshowing an enlargement of the LED chip of FIG. 13. As shown in FIG. 13or FIG. 14, the semiconductor device includes a unit board 301, an LEDchip 302, and a driver IC chip 303. The LED chip 302 includeslight-emitting parts 304, discrete electrodes 305, and electrode pads306. The electrode pads 306 of the LED chip 302 and the electrode pads307 of the bonding IC chip 303 are connected by bonding wires 308.Further, electrode pads 309 of the driver IC chip 303 and electrode pads310 of the unit board 301 are connected by bonding wires 311.

However, in the aforesaid conventional semiconductor device, a surfacearea of electrode pads 306 (e.g., of the order of 100 μm×100 μm) islarger than the surface area occupied by the light-emitting parts 304 onthe LED chip 302. Therefore, as long as the electrode pads 306 areprovided, it is difficult to reduce the chip width of the LED chip 302,and difficult to reduce the material cost of the LED chip 302.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide asemiconductor device which permits a major reduction of material cost,an LED print head using this semiconductor device, an image-formingapparatus using this LED print head, and a method of manufacturing thesemiconductor device.

A semiconductor device according to the present invention includes asubstrate, and a semiconductor thin film bonded to the substrate. Thesemiconductor thin film includes a plurality of discrete operatingregions, each of which has an operating layer, and an element isolatingregion, which is a thinned region of said semiconductor thin filmmutually isolating the operating layers of the plurality of discreteoperating regions.

An LED print head according to the present invention includes the abovesemiconductor device and a holder for holding the semiconductor device.

An image-forming according to the present invention includes the aboveLED print head, and a photosensitive body installed facing the LED printhead.

A method of manufacturing a semiconductor device according to thepresent invention includes forming a semiconductor thin film including aplurality of discrete operating regions, each of which has an operatinglayer, on a first substrate such that the semiconductor thin film can beseparated from first substrate; bonding the semiconductor thin filmwhich has been separated from the first substrate to a second substrate;and forming an element isolating region by etching a region other thanthe plurality of discrete operating regions of the semiconductor thinfilm bonded to the second substrate so as to mutually isolate theoperating layers of the plurality of discrete operating regions.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a perspective view schematically showing the construction of asemiconductor device according to a first embodiment of the presentinvention;

FIG. 2 is a perspective view schematically showing a driver IC chip,metal layer, and LED epitaxial film of the semiconductor device of FIG.1;

FIG. 3 is a cross-sectional view schematically showing a section througha line S₃-S₃ in the semiconductor device of FIG. 1;

FIG. 4 is a cross-sectional view schematically showing process formanufacturing the semiconductor device according to the firstembodiment;

FIG. 5 is a cross-sectional view schematically showing process formanufacturing the semiconductor device according to the firstembodiment;

FIG. 6 is a perspective view schematically showing the construction of asemiconductor device in a comparative example;

FIG. 7 is a perspective view schematically showing a driver IC chip,metal layer, and LED epitaxial film of the semiconductor device of FIG.6;

FIG. 8 is a cross-sectional view schematically showing a section througha line S₈-S₈ in the semiconductor device of FIG. 6;

FIG. 9 is a perspective view schematically showing the construction of asemiconductor device according to a second embodiment of the invention;

FIG. 10 is a cross-sectional view schematically showing a sectionthrough a line S₁₀-S₁₀ in the semiconductor device of FIG. 9;

FIG. 11 is a cross-sectional view schematically showing the constructionof an LED print head according to a third embodiment of the presentinvention;

FIG. 12 is a cross-sectional view schematically showing the constructionof an image-forming apparatus according to a fourth embodiment of thepresent invention;

FIG. 13 is a perspective view schematically showing a conventionalsemiconductor device; and

FIG. 14 is a perspective view showing an enlargement of part of an LEDchip in the semiconductor device of FIG. 13.

DETAILED DESCRIPTION OF THE INVENTION

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications will become apparent to those skilled in the art from thedetailed description.

First Embodiment

FIG. 1 is a perspective view schematically showing the construction of asemiconductor device according to a first embodiment of the presentinvention. FIG. 2 is a perspective view showing a driver IC chip, metallayer, and LED epitaxial film of the semiconductor device of FIG. 1, andFIG. 3 is a cross-sectional view schematically showing a section througha line S₃-S₃ in the semiconductor device of FIG. 1.

As shown in FIG. 1, FIG. 2, or FIG. 3, the semiconductor deviceaccording to the first embodiment includes a unit board 11, a driver ICchip 12 fixed on the unit board 11, a metal layer 13 formed on thedriver IC chip 12, and an LED epitaxial film 14 which is a semiconductorthin film bonded on the metal layer 13.

The driver IC chip 12 is an Si substrate in which an LED control driverIC is formed. Plural electrode terminals 12 a and plural electrodeterminals 12 b connected to the driver IC are provided on the surface ofthe driver IC chip 12.

The LED epitaxial film 14 includes a plurality of discrete operatingregions (light-emitting parts, i.e., LEDs) 14 a and an element isolatingregion 14 b which electrically isolates the plurality of discreteoperating regions 14 a from each other. The element isolating region 14b is a region wherein the LED epitaxial film 14 is etched to a shallowerdepth than the thickness of the LED epitaxial film 14, and is a thinnerregion than the plurality of discrete operating regions 14 a. The LEDepitaxial film 14, as shown in FIG. 3, has a multilayer semiconductorepitaxial structure wherein a lower contact layer 21, a lower claddinglayer 22, an activation layer 23 as an operating layer, an uppercladding layer 24, and an upper contact layer 25 are provided in thatorder from the side of the driver IC chip 12. For example, the lowercontact layer 21 is an n-GaAs layer, the lower cladding layer 22 is ann-Al_(z)Ga_(1-z)As layer, the activation layer 23 is an Al_(y)Ga_(1-y)Aslayer, the upper cladding layer 24 is a p-Al_(x)Ga_(1-x)As layer, andthe upper contact layer 25 is a p-GaAs layer. Herein, the values of x,y, and z are respectively set within a range from zero to unity so as toobtain high light-emitting efficiency. The epitaxial layers forming theLED epitaxial film 14 are not limited to the aforesaid example.

The thickness T of the LED epitaxial film 14 may be selected from amongvarious thicknesses, but the thickness T may be made as thin as about 2μm. The etching depth required to isolate the light-emitting regions 14a may be to immediately above the activation layer 23 (when theactivation layer 23 is non-doped), or may be to below a top surface ofthe lower cladding layer 22. FIG. 3 shows the case where etching hasbeen performed to below the top surface of the lower cladding layer 22.

The metal layer 13 is formed, for example, in a region where the driverIC is formed, or a region adjacent to the region where the driver IC isformed, on the surface of the driver IC chip 12, wherein the regionwhere the driver IC is formed is a flat region. The metal layer 13 may,for example, be palladium, gold, or the like. The metal layer 13 may,for example, be formed by chemical vapor deposition or sputtering. TheLED epitaxial film 14 is bonded to the surface of the metal layer 13.The metal layer 13 has the function of fixing the LED epitaxial film 14,which is stuck to the metal layer 13, to the driver IC chip 12, and thefunction of electrically connecting a common terminal region (lowercontact layer 21) on the lower surface of the LED epitaxial film 14 anda common terminal region of the driver IC chip 12 (not shown). Ohmiccontacts are preferably formed between the metal layer 13 and the lowercontact layer 21 in the LED epitaxial film 14, and between the metallayer 13 and the common terminal region of the driver IC chip 12. Thebonding of the LED epitaxial film 14 to the metal layer 13 may, forexample, be achieved by intermolecular forces between the epitaxial filmand the metal layer, and by a reaction between the epitaxial film andthe metal layer (atomic rearrangement of interface).

As shown in FIG. 1 and FIG. 3, the semiconductor device according to thefirst embodiment further includes discrete interconnection layers (thinfilm interconnections) 32 extending from tops of the discrete operatingregions 14 a through the element isolating region 14 b to the driver ICchip 12. As shown in FIG. 3, an interlayer insulating film 31 isprovided between the LED epitaxial film 14 and the discreteinterconnection layer 32, the discrete interconnection layer 32 beingconnected to the upper contact layer 25 via openings 31 a in theinterlayer insulating film 31. The discrete interconnection layers 32electrically connect the upper surfaces of the light-emitting part 14 aof the LED epitaxial film 14, and the discrete terminal regions 12 a ofthe IC chip 12. The discrete interconnection layer 32 is a thin filmmetal interconnection or the like, e.g., an Au layer, a Pd layer, aPd/Au laminated layer, an Al layer, or a polysilicon layer. A pluralityof discrete interconnection layers 32 may be formed all at once using aphotolithography technique.

The unit board 11 has electrode pads 11 a on its surface. The electrodeterminals 12 b of the driver IC chip 12 and the electrode pads 11 a ofthe unit board 11 are connected by bonding wires 33.

Next, the method of manufacturing a semiconductor device according tothe first embodiment will be described. FIG. 4 and FIG. 5 arecross-sectional views schematically showing process for manufacturing asemiconductor device according to the first embodiment. As shown in FIG.4, first, a separation layer (sacrificial layer) 112 is formed on amanufacturing substrate (e.g., a GaAs substrate) 111 for forming the LEDepitaxial layer 114, and the LED epitaxial layer (semiconductor thinfilm) 114 including a plurality of discrete operating regions is formedon the sacrificial layer 112. The LED epitaxial layer 114 can bemanufactured by the metal oxide chemical vapor deposition method (MOVCDmethod), metal oxide vapor phase epitaxy method (MOVPE method),molecular beam epitaxy method (MBE method), or the like known in theart. The LED epitaxial layer 114 includes an n-GaAs layer 121, ann-Al_(z)Ga_(1-z)As layer 122, an Al_(y)Ga_(1-y)As layer 123, ap-Al_(x)Ga_(1-x)As layer 124, and a p-GaAs layer 125, which correspondto the lower contact layer 21, the lower cladding layer 22, theactivation layer 23, the upper cladding layer 24, and the upper contactlayer 25, respectively.

On the other hand, as shown in FIG. 1, the metal layer 13 is formed bychemical vapor deposition or sputtering on the driver IC chip (Sisubstrate) 12. Next, the LED epitaxial film (the LED epitaxial layer114) is obtained by etching part of the LED epitaxial layer 114 and thesacrificial layer 112 as shown in FIG. 5 and peeling (i.e., separating)the LED epitaxial layer 114 away from the GaAs substrate 111 by thechemical lift-off method, and the LED epitaxial film is bonded to themetal layer 13 of the driver IC chip 12.

Next, as shown in FIG. 1, an element isolating region 14 b whichelectrically isolates the plurality of discrete operating regions 14 a,is formed by etching a region other than the plurality of discreteoperating regions 14 a of the LED epitaxial film 14 bonded to the driverIC chip to a shallower depth than the thickness of the LED epitaxialfilm 14. In the etching, a resist is used to prevent etching of thediscrete operating regions 14 a and etch the element isolating region 14b. The etching solution used may, for example, be a solution ofphosphoric acid, and the etching temperature may, for example, be of theorder of 30° C. The etching time is determined based on a pre-obtainedetching rate and the desired etching depth. However, the etchingconditions are not limited to these examples. Next, the interlayerinsulating film 31 is formed, and the discrete interconnection layers 32extending from the tops of the discrete operating regions 14 a over theelement isolating region 14 b to the tops of the discrete electrodeterminals 12 a of the driver IC chip 12, are formed by aphotolithography technique.

As described above, in the semiconductor device according to the firstembodiment, the thin LED epitaxial film 14 which has a thickness ofseveral micrometers is used as the light-emitting element device, so thelight-emitting parts 14 a of the LED epitaxial film 14 and the discreteelectrode terminals 12 a of the driver IC chip 12 can be connected bythe discrete interconnection layers 32. Therefore, it is unnecessary toprovide electrode pads on the LED epitaxial film 14, and due to thereduction in the surface area of the LED epitaxial film 14, majormaterial cost savings can be achieved.

In the semiconductor device according to the first embodiment, theelement isolating region 14 b is formed so that there is no reduction inthe contact area between the LED epitaxial film 14 and the driver ICchip 12, hence the electrical properties of the discrete operatingregions 14 a can be enhanced without reducing the adhesion strength ofthe LED epitaxial film 14 on the driver IC chip 12.

Also, in the semiconductor device according to the first embodiment, thecontact surface area of the LED epitaxial film 14 with the driver ICchip 12 is large, so contact resistance can be reduced. Herein, forreference purposes, a comparison will be made with the case where theelements are separated by completely etching a region other than thelight-emitting part of the LED epitaxial film (comparative example).FIG. 6 is a perspective view schematically showing the construction ofthe semiconductor device according to this comparative example. FIG. 7is a perspective view showing the driver IC chip, metal layer and LEDepitaxial film of the semiconductor device of FIG. 6, and FIG. 8 is across-sectional view schematically showing a section through a lineS₈-S₈ in the semiconductor device of FIG. 6. In the case of thecomparative example shown in FIG. 6 to FIG. 8, as the semiconductor thinfilm is only the light emitting parts 14 a, the contact area isextremely small, but the contact surface area of the LED epitaxial film14 of the semiconductor device in the first embodiment is the sum of thesurface areas of the light-emitting parts 14 a and the element isolatingregion 14 b, so the contact surface area is extremely large.

In the semiconductor device according to the first embodiment, the metallayer 13 is disposed on the undersurface of the LED epitaxial film 14,so light emitted from the light-emitting parts 14 a in the direction ofthe undersurface (i.e., towards the driver IC chip 12) can be extractedin the surface direction as light reflected by the metal layer 13, andthe power of the emitted light is thus increased.

Further, in the semiconductor device according to the first embodiment,part of the LED epitaxial film 14 remains on the element isolatingregion 14 b of the LED epitaxial film 14, so steps on the LED epitaxialfilm 14 are reduced, and the occurrence of breaks in thin filminterconnections such as the discrete interconnection layers can bereduced.

In the aforesaid description, the case was described where thesemiconductor device was a light-emitting element array, but the presentinvention may be applied also to a semiconductor device other than alight-emitting element array.

Second Embodiment

FIG. 9 is a perspective view schematically showing the construction of asemiconductor device according to a second embodiment of the presentinvention. FIG. 10 is a cross-sectional view schematically showing asection through a line S₁₀-S₁₀ in the semiconductor device of FIG. 9.

As shown in FIG. 9 or FIG. 10, the semiconductor device according to thesecond embodiment includes a unit board 51, a driver IC chip 52 fixed tothe unit board 51, and an LED epitaxial film 54 which is a semiconductorthin film bonded to the driver IC chip 52. The driver IC chip 52 and theLED epitaxial film 54 are bonded by an adhesive 53.

The LED epitaxial film 54 includes a plurality of discrete operatingregions (light-emitting regions, i.e., LEDs) 54 a, and an elementisolating region 54 b which electrically isolates the plurality ofdiscrete operating regions 54 a from each other. The element isolatingregion 54 b is a region wherein the LED epitaxial film 54 has beenetched to a shallower depth than the thickness of the LED epitaxial film54, and is a thinner region than the plurality of discrete operatingregions 54 a. The LED epitaxial film 54, as shown in FIG. 10, has amultilayer semiconductor epitaxial structure including, in order fromthe side of the driver IC chip 52, a lower contact layer 61, a lowercladding layer 62, an activation layer 63, an upper cladding layer 64,and an upper contact layer 65. For example, the lower contact layer 61is an n-GaAs layer, the lower cladding layer 62 is an n-Al_(z)Ga_(1-z)Aslayer, the activation layer 63 is an Al_(y)Ga_(1-y)As layer, the uppercladding layer 64 is a p-Al_(x)Ga_(1-x)As layer, and the upper contactlayer 65 is a p-GaAs layer. Herein, the values of x, y, and z arerespectively set within a range from zero to unity so as to obtain highlight-emitting efficiency. The epitaxial layers forming the LEDepitaxial film 54 are not limited to the aforesaid example.

The thickness T of the LED epitaxial film 54 may be selected from amongvarious thicknesses, but the thickness T may be made as thin as about 2μm. Further, in the second embodiment, the element isolating region 54 bis formed from part of the lower contact layer 61. Here, the case isshown where the etching depth to electrically isolate the light-emittingparts 54 extends to midway in the lower contact layer 61. As a result,the thickness of the lower contact layer 61 is made larger than that ofthe contact layer 21 in the first embodiment. The thickness of the lowercontact layer 61 may be set within a range in which etching can bestopped midway in the lower contact layer 61.

As shown in FIG. 9 and FIG. 10, the semiconductor device according tothe second embodiment further includes discrete interconnection layers(thin film interconnections) 72 which extend from the tops of thediscrete operating regions 54 a over the element isolating region 54 bto the tops of the driver IC chip 52. As shown in FIG. 10, an interlayerinsulating film 71 is provided between the LED epitaxial film 54 and thediscrete interconnection layer 72, the discrete interconnection layer 72being connected to the upper contact layer 65 via openings 71 a in theinterlayer insulating film 71. The discrete interconnection layers 72electrically connect the upper surfaces of the light-emitting parts ofthe LED epitaxial film 54 with discrete terminal regions 52 a of thedriver IC chip 52.

The unit board 51 has electrode pads 51 a on its surface. The electrodeterminals 52 b of the driver IC chip 52 and the electrode pads 51 a ofthe unit board 51 are connected by bonding wires 73.

As shown in FIG. 9 and FIG. 10, an electrode pad 74 is provided on thelower contact layer 61, the electrode pad 74, and a common electrodeterminal 52 c of the driver IC chip 52 being connected by a commoninterconnection layer (thin film interconnection) 75. The discreteinterconnection layers 72 and the common interconnection layer 75 may,for example, be thin film metal interconnections, and may be formed allat once by a photolithography technique. Hence, in the secondembodiment, both the discrete interconnection layers 72 and the commoninterconnection layer 75 are provided on the upper side of the LEDepitaxial film 54, so the contact resistance of the underside of the LEDepitaxial film 54 does not have to be taken into account. As a result,there is more freedom of choice in the adhesive 53 used to improve thebonding strength of the LED epitaxial film 54, and the adhesion strengthcan be enhanced. Also, as the whole of the LED epitaxial film 54 isconnected by the lower contact layer 61, it can be widened by the commonelectrode pad 74 and the contact resistance can be reduced compared tothe first embodiment.

In the semiconductor device according to the second embodiment, in thesame way as in the first embodiment, major material cost reductions,improved adhesion strength of the LED epitaxial film 54 and improvedelectrical properties of the discrete operating regions can be obtained.Except for the above-mentioned points, the semiconductor device of thesecond embodiment is the same as that of the first embodiment.

Third Embodiment

FIG. 11 is a cross-sectional view schematically showing the constructionof an LED print head according to a third embodiment of the presentinvention.

As shown in FIG. 11, an LED print head 100 of the third embodimentincludes a base member 101, an LED unit 102 fixed to the base member101, a rod lens array 103 containing an alignment of plural rod-shapedoptical elements, a holder 104 which holds the rod lens array 103, and aclamp 105 which grips and fixes these components 101-104. In the figure,101 a and 104 a are openings through which the clamp 105 penetrates. TheLED unit 102 includes an LED array chip 102 a. The LED array chip 102 aincludes one or more of the semiconductor devices of the first or secondembodiment. Light generated by the LED array chip 102 a passes throughthe rod lens array 103 and is emitted to the outside. The LED print head100 is used as an exposure device for forming an electrostatic latentimage in an electrophotographic printer or electrophotographic copier.The construction of the LED print head including the semiconductordevice of the first or second embodiment is not limited to that shown inFIG. 11.

In the LED print head of the third embodiment, the LED unit 102 uses thesemiconductor device of the first or second embodiment, so excellentlight emission properties, device compactness and major material costreductions can be achieved.

Fourth Embodiment

FIG. 12 is a cross-sectional view schematically showing the constructionof an image-forming apparatus according to a fourth embodiment of thepresent invention.

As shown in FIG. 12, an image-forming apparatus 200 of the fourthembodiment includes four process units 201-204 which form yellow (Y),magenta (M), cyan (C) and black (K) images by an electrophotographictechnique. The process units 201-204 are tandemly arranged in thetransport path of a recording medium 205. The process units 201-204 eachinclude a photosensitive drum 203 a which functions as an image carrier,a charging device 203 b which is disposed near the photosensitive drum203 a and charges the surface of the photosensitive drum 203 a, and anexposure device 203 c which forms an electrostatic latent image byselectively irradiating the surface of the charged photosensitive drum203 a with light. The exposure device 203 c is used for the LED printhead 100 described in the third embodiment, and contains thesemiconductor device described in the first or second embodiment.

The image-forming apparatus 200 also includes developing devices 203 dwhich transport toner to the surface of the photosensitive drums 203 onwhich the electrostatic latent image is formed, and cleaning devices 203e which removes toner remaining on the surfaces of the photosensitivedrums 203 a. The photosensitive drums 203 a each are rotated in thedirection of the arrow by a drive mechanism including a power source,not shown, and gears. The image-forming apparatus 200 further includes apaper cassette 206 which houses the recording medium 205 such as paperor the like, and a hopping roller 207 which separates and transports therecording medium 205 one sheet at a time. Pinch rollers 208, 209, andresist rollers 210, 211 which correct the skew of the recording medium205 together with the pinch rollers 208, 209 and transport it to theprocess units 201-204, are installed downstream of the hopping roller207 in the transport direction of the recording medium 205. The hoppingroller 207 and resist rollers 210, 211 rotate in synchronism with thepower source, not shown.

The image-forming apparatus 200 further includes transfer rollers 212disposed facing the photosensitive drums 203 a. The transfer rollers 212each are formed of semi-electrically conducting rubber or the like. Thepotentials of the photosensitive drum 203 a and transfer roller 212 areset so that the toner image on the photosensitive drum 203 a istransferred to the recording medium 205. Also, the image-formingapparatus is provided with a fixing device 213 which heats andpressurizes the toner image on the recording medium 205, and rollers214, 216 and 215, 217 for ejecting the recording medium 205 which haspassed through the fixing device 213.

The recording medium 205 stacked in the paper cassette 206 is separatedand transported one sheet at a time by the hopping roller 207. Therecording medium 205 passes through the resist rollers 210, 211 andpinch rollers 208, 209, and through the process units 201-204 in thatorder. In the process units 201-204, the recording medium 205 passesbetween the photosensitive drums 203 a and the transfer rollers 212,whereupon color toner images are transferred in sequence, andheated/pressurized by the fixing device 213 so that the color tonerimages are fixed on the recording medium 205. Subsequently, therecording medium 205 is ejected to a stacker 218 by the ejectingrollers. The construction of the image-forming apparatus including thesemiconductor device of the first or second embodiment or the LED printhead of the third embodiment, is not limited to that shown in FIG. 12.

In the image-forming apparatus 200 of the fourth embodiment, the LEDprint head 100 of the third embodiment is used, so a high-quality imagecan be formed by the excellent light-emitting properties of the exposuredevice. Also, space is saved due to the compactness of the exposuredevice, and major material cost reductions can be achieved. The presentinvention may also be applied to a monochrome printer, but aparticularly large advantage is obtained in the case of a full colorprinter having plural exposure units.

1. A semiconductor device comprising: a substrate including a metallayer as an upper layer; a semiconductor thin film having a firstprincipal surface as a bonding area and a second principal surface whichis an opposite surface of said first principal surface, said firstprincipal surface of said semiconductor thin film being placed above andbonded to a top surface of said substrate having the metal layer, anarea of said bonding area of said first principal surface of saidsemiconductor thin film being larger than an area of said secondprincipal surface of said semiconductor thin film; an interlayerinsulating film disposed so as to cover said semiconductor thin film andsaid metal layer, said interlayer insulating film having an openingformed on a top contact area of said second principal surface; and adiscrete interconnection layer which extends from and on said topcontact area, through said opening, through and on said interlayerinsulating film, and to and on said substrate, so as to electricallycouple said top contact area to said substrate.
 2. The semiconductordevice according to claim 1, wherein said semiconductor thin filmincludes a discrete operating region which has an operating layer, and athinner region which is a thinned region of said semiconductor thinfilm, said thinned region forming a step of a reduced height on saidsubstrate.
 3. The semiconductor device according to claim 1, whereinsaid discrete interconnection layer is in direct contact with said topcontact area, said interlayer insulating film, and said substrate,respectively.
 4. The semiconductor device according to claim 1, whereinsaid substrate is a driving circuit substrate which includes anintegrated circuit.
 5. The semiconductor device according to claim 1,wherein said semiconductor thin film comprises a multilayersemiconductor epitaxial structure including, in order from a side ofsaid substrate, a lower contact layer, a lower cladding layer, anactivation layer as said operating layer, an upper cladding layer, andan upper contact layer, wherein said thinner region is an elementisolating region that includes said lower contact layer and part of saidlower cladding layer.
 6. The semiconductor device according to claim 1,wherein said semiconductor thin film comprises a multilayersemiconductor epitaxial structure including, in order from a side ofsaid substrate, a lower contact layer, a lower cladding layer, anactivation layer as said operating layer, an upper cladding layer and anupper contact layer, wherein said thinner region is an element isolatingregion that includes part of said lower contact layer.
 7. Thesemiconductor device according to claim 6 further comprising: a commoninterconnection layer extending from a top of said lower contact layerof said element isolating region to a top of said substrate.
 8. Thesemiconductor device according to claim 1 further comprising: a metallayer interposed between said substrate and said semiconductor thinfilm.
 9. The semiconductor device according to claim 1, wherein saidsemiconductor thin film is bonded using an adhesive.
 10. Thesemiconductor device according to claim 1, wherein said discreteoperating region comprises a light-emitting element.
 11. Thesemiconductor device according to claim 1, wherein said semiconductorthin film includes a plurality of discrete operating regions, and saidthinner region isolates said discrete operating regions mutually. 12.The semiconductor device according to claim 2, wherein said discreteinterconnection layer crosses edges of said discrete operating regionand said thinner region.
 13. An LED print head comprising: saidsemiconductor device according to claim 1; and a holder for holding saidsemiconductor device.
 14. An image-forming apparatus comprising: saidLED print head according to claim 11; and a photosensitive bodyinstalled facing said LED print head.